The present invention relates generally to an internal combustion engine. More specifically, the present invention relates to an internal combustion engine having horizontally opposed pistons within one cylinder.
Engines, in general, operate as a function of their geometry. Typically, the workings of the engine components are fixed in relation during operation. This relation is not capable of changing during various operating conditions of the engine. The relationship of the various components are thus not optimized over the full operating range of the engine. Typically, the geometry is optimized in a narrow operating range of the engine.
Various engines having horizontally opposed pistons within one cylinder are known. Engines having two horizontally opposed pistons are suitable for many applications. Such engines may be used in four cycle and two cycle applications. The advantage of using two pistons in a single cylinder is that the compression within in the cylinder may be altered by moving one piston with respect to the other. The movement of one piston with respect to the other is known as changing the phase of the pistons. It is desirable to change the phase of the pistons based on the relative speed of the crankshaft. In this manner, the compression of the engine may be changed as desired based on operating conditions of the engine.
One drawback to using two pistons in a single cylinder is the positioning of the valves. The valves are commonly oriented in a direction perpendicular to the axis of the cylinder. This orientation increases the overall size of the block. For many applications space is limited. A larger block also increases the weight of the engine. For reasons of economy, reducing weight is desirable.
Another disadvantage to horizontally opposed pistons within a single cylinder is that a significant amount of dead space is formed around the location of each valve and the location of the spark plug. In many configurations, the valves are located on opposite sides of the cylinder or are spaced apart on the same side of the cylinder. When closed, the valves are spaced back from the cylinder walls to prevent wear. The area directly adjacent the valves is the "dead space". Dead space is the space within the cylinder through which the pistons do not travel. Dead space is an irregular shape and may facilitate the build-up of undesired emissions gases during combustion. Reduction of dead space is therefore desirable.
One example of an engine having horizontally opposed pistons is described in U.S. Pat. No. 1,889,946. The intake and exhaust valves are located in a common dead space located adjacent each other. The dead space in this configuration is quite large and thus undesirable.